This application is a 371 of PCT/DE98/01438, filed on May 20, 1998.
1. Field of the Invention
The invention is directed to an immersion nozzle of a metallurgic vessel which is arranged upstream of a continuous casting mold and which is constructed as a single-piece structural component part and has, in the mouth area, a slit-shaped pour-out opening whose length is several times greater than its width. The invention further relates to a method for producing an immersion nozzle of this type.
2. Discussion of the Prior Art
DE 37 09 188 C2 discloses an immersion nozzle for continuous casting molds which comprises at least two structural component parts, wherein the part projecting into the continuous casting mold is narrow in a plane perpendicular thereto and, in this respect, has a length-to-width ratio of 20:1 to 80:1.
Both the upper and lower longitudinal portions must be produced in a costly manner with special core segments which can be divided in this location.
DE-OS 24 28 060 discloses a continuous method for the continuous casting of steel in which steel is guided via a pour pipe into a substantially rectangular mold. The pour pipe has lateral outlet openings which are directed downward.
It is disadvantageous that a flow divider is provided in the center of the mouth and, in case of the slightest irregularities, the flow of steel is deflected by the flow divider preferably in one direction and, moreover, a central flow-in of the steel is prevented.
U.S. Pat. No. 3,991,815 discloses a pour pipe or casting tube which has, in the mouth area, a bottleneck-shaped narrowing and bore holes which are directed toward the rear at the sides adjacent to the central flow-out opening. This submerged casting tube, which is essentially provided for billet plants, disadvantageously divides the flow into three mutually independent individual flows.
It is the object of the invention to provide an immersion nozzle for a continuous slab casting plant which has a simply designed construction and long life and which guides the molten metal into a continuous slab casting mold with low turbulence and penetration depth, as well as a method for producing an immersion nozzle of this type.
According to the invention, the immersion nozzle which is constructed as a cylinder, has a continuous slit in its base which extends into the side wall. The cross-sectional shape of the cylinder can be circular, oval, or bone-shaped, i.e., oval with a bulge.
The base of the cylindrical immersion nozzle is dish-shaped or is beveled and accordingly terminates in a wedge-shaped manner in the direction of the slit.
The slit has side walls which are basically arranged so as to extend parallel to one another in a straight-line. In an advantageous embodiment, the slit-shaped pour-out opening is wedge-shaped with the large opening in the center of the slit. In a further embodiment, the slit-shaped pour-out opening is wider in the area of the side wall than in the center of the mouth. The shape of the side wall follows a curved shape having turning or inflection points in the area of the base at both sides of the center axis. In a particularly advantageous construction, the extension of the slit in the side walls is changeable. The change in length can be achieved gradually by means of insert pieces which can be inserted in the base of the slit.
A continuous change in the slit length is achieved by means of a sleeve which encloses the immersion nozzle in a displaceable manner. In this respect, the length of the sleeve is either dimensioned so as to be so short that the sleeve is completely immersed in the melt or, in another construction, the sleeve has a length which extends until close to the metallurgic vessel at one end, wherein sealing means are provided between the sleeve and the submerged nozzle in order to prevent a flow of unwanted air into the liquid melt.
In order to influence the slit length at both ends of the slit, the sleeve is beveled at its mouth end and is constructed so as to be rotatable in addition to the axial displacement.
The production of the body can be influenced in a particular way by means of the especially simple shape of the immersion nozzle with its cylindrical wall.
According to the invention, during the production of an immersion nozzle the outer shape body or outer mold body is oriented upward by the end to be fastened subsequently to the metallurgic vessel. A plate is inserted in the base area corresponding to the intended slit. The negative shapes for the subsequent base shape, namely, the dish base or wedge, are already present in the outer mold body or can be added as a structural component part.
The core is inserted into the cavity from the top in conformity to dimensions. After the core is fixed, the refractory material is introduced and correspondingly treated, that is, substantially solidified. Taking into account a required conicity, or amount of taper, in the basic cylindrical shape of the immersion nozzle, the core as well as the outer mold body can be removed from the finished immersion nozzle in a simple manner.
Due to the construction of the base with the continuous slit as suggested according to the invention, the liquid melt exits the immersion nozzle during operation in a shape and at a speed which allows a particularly small penetration of the fed melt into the melt already located in the mold. In this way, only very slight turbulence occurs. The melt volumes are unified in a particularly short time and flow in a piston-shaped or bulb-shaped stream at the predetermined take-off speed in the steel strand surrounded by the strand shell.
The immersion nozzle arranged in front is suitable for slabs and billets because the melt exiting from the immersion nozzle has only a low kinetic energy. The melt exiting the immersion nozzle from the slit spreads out in a cloudlike manner with only a small penetration depth in all directions.
After flowing a short distance, the fresh melt flowing into the crater assumes the shape of a bulb flow and this has positive effects on the quality of the product, especially on the purity of the steel. Further, the homogeneity is improved and impurities are reduced.
The steel generated in this way has an especially high degree of purity.
Another result of the small penetration depth in the crater is the possibility that only a short mixing length is caused in case of a change in quality during pouring on the continuous casting plant, so that only a short piece of slab steel of unwanted quality is generated.
An example of the invention is shown in the accompanying drawings.